The present invention starts from a fuel injection valve according to the type of the main claim.
A fuel injection valve having a valve closing body that can be activated by an activation device by means of a valve needle and that interacts with a valve seat surface to produce a seat is known from German Patent 38 00 203 C2. In this case the activation device for producing a valve needle lift has two piezoelectric bending elements that bend when the activation device is activated. In this context the bending elements are oriented in their longitudinal direction perpendicular to the direction of movement of the valve closing body. Each of the activating elements has a ceramic plate arranged between two conductive films. The ceramic plate and the conductive films are thus stacked in the direction of movement of the valve closing body. To activate the activation device, a voltage applied between the conductive films acts on the ceramic plate causing the ceramic plate to bend. The bending is transmitted to the valve needle via a stop disk causing the valve closing body to lift away from the valve seat surface and the seat to open. A greater valve needle lift can be produced by stacking bending elements, which are arranged so that they bend convexly or concavely relative to one another.
In the fuel injection valve known from German Patent 38 00 203 C2, it is disadvantageous that the ceramic plate and the conductive films are layered one above the other in the direction of movement of the valve closing body, as a result of which each bending element only produces a small valve needle lift and only a small force can be applied for opening the valve needle. A very large number of stacked bending elements is therefore necessary to achieve an appropriate valve needle lift.
A further disadvantage is that the bending elements have a central bore through which the valve needle projects, so that when the bending elements are activated, high bending stresses occur in the central area of the bending elements, thereby limiting the valve needle lift attainable by the bending elements. Moreover, during extremely frequent activation of the fuel injection valve, high frictional forces are produced in the area of the central bore due to the friction between the valve needle and the bending elements, the insulating films being required at the same time to be electrically insulated from one another. The fuel injection valve proposed in German Patent 38 00 203 C2 is therefore expensive to manufacture and cannot be used as a quick-switching fuel injection valve or as a high-pressure fuel injection valve.
From Japanese Patent Application 62-121 860 A, a fuel injection valve having two bending elements arranged parallel to a valve axis is known. As in German Patent 38 00 203 C2, the bending elements are made of layers arranged parallel to a substrate.
By contrast, the fuel injection valve of the present invention having the characterizing features of the main claim has the advantage that a large lift is produced by the piezo elements stacked in a longitudinal direction of the bending element. Moreover, the fuel injection valve of the present invention can also be used as a quick-switching fuel injection valve and/or as a high-pressure fuel injection valve.
Advantageous developments of the fuel injection valve indicated in the main claim are possible by implementing the measures cited in the subclaims.
The activation device advantageously has a piezoelectric second bending element made of a plurality of piezo elements stacked in the longitudinal direction of the second bending element, the two bending elements being arranged staggered with respect to one another. This enables the valve needle""s lift produced by the activation device to be increased.
It is furthermore advantageous if, when the activation device is activated, the second bending element bends in the opposite direction to the first bending element. This makes it possible to economize on additional support assemblies and intermediate plates.
It is advantageous if the activation device has a tie rod that connects the bending elements to the valve needle by friction. By this means the activation device acts on the valve needle without adversely affecting the function of the bending elements. It is also advantageous if the valve needle is surrounded at least in sections by a valve needle sleeve and for the valve needle sleeve to have an attachment surface to which the tie rod is attached via a welded joint. Thus, a simple conformation of the attachment is achieved. Advantageously, the tie rod encloses the bending elements and the free ends of the tie rod are connected to the valve needle or the valve needle sleeve.
Advantageously, the bending elements in a starting position are oriented essentially parallel to a valve axis, resulting in an installation-favorable variant.
Furthermore, it is advantageous if the bending elements for acting upon the seat are bent relative to one another with an initial tension in a closed position of the fuel injection valve. This makes it possible to economize on additional components. The initial tension can also be reinforced by an initial tension element, in particular a spring steel strip.